of the bone. (Anatomical
Museum, University of Edinburgh.)]

TUBERCULOUS DISEASE

The tuberculous diseases of bone result from infection of the marrow or
periosteum by tubercle bacilli conveyed through the arteries; it is
exceedingly rare for tubercle to appear in bone as a primary infection,
the bacilli being usually derived from some pre-existing focus in the
bronchial glands or elsewhere. According to the observations of John
Fraser, 60 per cent. of the cases of bone and joint tubercle in children
are due to the bovine bacillus, 37 per cent. to the human variety, and
in 3 per cent. both types are present.

Tuberculous disease in bone is characterised by its insidious onset and
slow progress, and by the frequency with which it is associated with
disease of the adjacent joint.

#Periosteal tuberculosis# is met with in the ribs, sternum, vertebral
column, skull, and less frequently in the long bones of the limbs. It
may originate in the periosteum, or may spread thence from the marrow,
or from synovial membrane.

_In superficial bones_, such as the sternum, the formation of
tuberculous granulation tissue in the deeper layer of the periosteum,
and its subsequent caseation and liquefaction, is attended by the
insidious development of a doughy swelling, which is not as a rule
painful, although tender on pressure. While the swelling often remains
quiescent for some time, it tends to increase in size, to become boggy
or fluctuating, and to assume the characters of a cold abscess. The pus
perforates the fibrous layer of the periosteum, invading and infecting
the overlying soft parts, its spread being influenced by the anatomical
arrangement of the tissues. The size of the abscess affords no
indication of the extent of the bone lesion from which it originates. As
the abscess reaches the surface, the skin becomes of a dusky red or
livid colour, is gradually thinned out, and finally sloughs, forming a
sinus. A probe passed into the sinus strikes carious bone. Small
sequestra may be found embedded in the granulation tissue. The sinus
persists as long as any active tubercle remains in the tissues, and is
apt to form an avenue for pyogenic infection.

_In deeply seated bones_, such as the upper end of the femur, the
formation of a cold abscess in the soft parts is often the first
evidence of the disease.

_Diagnosis._--Before the stage of cold abscess is reached, the localised
swelling is to be differentiated from a gum